Factors Affecting Progesterone in Milk for Pregnancy Diagnosis in Dairy Cattle

Abstract

Concentration of progesterone in milk was used to diagnose pregnancy in 508 dairy cows. Diagnosis of cows as pregnant and not pregnant by milk progesterone on day 21 post-breeding had 76 and 98% agreement, respectively, with diagnosis by palpation or return to oestrus. Overall agreement was 85%. Fourteen cows were classified as questionable. Of cows returning to oestrus after 30 days post-breeding, 64% were determined to be not pregnant by milk progesterone on day 21. Breed of cow did not affect the accuracy of diagnosis. Use of either extracted or non-extracted milk for progesterone analysis gave similar results for pregnancy diagnosis. Diagnosis by concentration of progesterone in milk was not improved by expressing progesterone as progesterone per unit fat or progesterone per milking. Pregnancy diagnosis by progesterone determination in milk at day 21 or day 23 post-breeding had a greater percentage agreement with diagnosis by palpation than diagnosis by milk progesterone on day 19, day 25, day 27, or day 29 post-breeding.